Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 153
Reclaimed Asphalt Pavement 153
SELECT 8 -10
RANDOM
SAMPLING
LOCATIONS
OBTAIN STOCKPILE SAMPLES
AASHTO T2
Size = 10 kg x (number of mix designs) + 5 kg
5 kg SPLIT REMAINDER
SAMPLE
AASHTO T248
COMBINE WITH OTHER
2.5 kg SPLIT 2.5 kg LOCATIONS TO CREATE
SAMPLE
REPRESENTATIVE SAMPLE
AASHTO T248
COMBINE WITH OTHER
BINDER CONTENT AND LOCATIONS TO CREATE
GRADATION FOR REPRESENTATIVE SAMPLE
BLENDING AND
VARIABILITY ANALYSIS
2.5 kg SPLIT REMAINDER
SAMPLE
AASHTO T248
CHARACTERIZE RAP CHARACTERIZE
BINDER PROPERTIES RAP AGGREGATE
IF REQUIRED PROPERTIES
VOLUMETRIC MIXTURE
DESIGN AND
PERFORMANCE ANALYSIS
Figure 9-2. Flow chart for recommended sampling of RAP stockpiles.
prepared. Figure 9-2 is a general flowchart for sampling a RAP stockpile for use in HMA mix-
ture design.
Blending and Variability
RAP variability is an important consideration in the design of HMA incorporating RAP. Many
agency specifications require mixtures with RAP to be produced to the same production tolerances
as mixtures made with all new materials. If highly variable RAP is used, then the HMA may not
meet production tolerances, resulting in lost production time, a penalty, or, in extreme cases, the
need to remove and replace the mixture. The amount of RAP that can be added without exceeding
OCR for page 154
154 A Manual for Design of Hot Mix Asphalt with Commentary
specification limits depends on the limits themselves, the variability of the RAP, the variability of
similar mixtures produced without RAP, and the consistency of the equipment adding the RAP.
Unfortunately, the calculation of maximum RAP content based on a variability analysis is quite
complicated and often some of the information required is uncertain or even unknown. For these
reasons, the approach recommended in this manual is somewhat simplified, but based soundly
on the basic statistical theory involved. It will provide engineers and technicians with reasonable
estimates of the amount of RAP that can be incorporated into a mix design without unaccept-
able increases in production variability. Two different methods can be used to determine the
maximum allowable RAP content based on variability: a graphical approach and the HMA Tools
spreadsheet. The same statistics are used in both cases, but HMA Tools is a more precise approach
that will often allow for somewhat higher RAP contents.
Because many state highway agencies already have specifications in place establishing allow-
able RAP contents in HMA mixtures, HMA Tools allows any RAP content in the design process.
If desired, HMA Tools can be used to perform the statistical analysis of RAP stockpiles and to
determine the maximum allowable RAP content. However, this is not required. Thus, the user
can enter any desired RAP content when using HMA Tools to develop mix designs.
RAP Binder Content and Aggregate Gradation:
Laboratory Procedures
The average and standard deviation of the binder content and aggregate gradation in the RAP
stockpiles are properties that must be measured to effectively design HMA with RAP. The 5 kg
sub-samples split from the sample taken at each sampling location are used for this analysis.
If reasonable estimates of the ignition oven correction factors for local aggregates can be made,
then the RAP binder content can be determined using an ignition oven, AASHTO T 308. The
gradation of the RAP aggregates is then determined using AASHTO T 30 after application of the
aggregate correction factors as described in AASHTO T 308. If correction factors for local aggregates
are unknown or highly variable, then the RAP binder content must be determined by solvent
extraction, AASHTO T 164. The gradation of the extracted aggregate is then determined using
AASHTO T 30. If desired, ignition oven correction factors can be established by performing both
analyses on split samples from at least three locations in the stockpile.
Determining Combined Gradation and Binder Content
The computation of blends for mixtures incorporating RAP is a little different than that for
mixtures made with all new stockpiles. When RAP is used, the RAP material that is added
includes both the RAP aggregate and the RAP binder. Since gradation data are based on the
weight of aggregate, and binder contents are based on the total weight, the stockpile percentages
must be adjusted for combined gradation analysis based on the amount of binder contained in
the RAP. In using HMA Tools to determine the composition of HMA mixes containing RAP,
data on the aggregate gradations--including the gradation of aggregate contained in the RAP--
is entered in the worksheet "RAP_Aggregates." Aggregate bulk and apparent specific gravity data
is also entered here, along with the asphalt binder content and specific gravity. Data for up to
four RAP stockpiles can be entered. General information for the mix--most importantly the tar-
get VMA and air void content--are entered in the worksheet "General." The actual composition
of the blend is entered in the worksheet "Trial_Blends," which then lists the combined gradation
and various other data for the mix. The example below illustrates the use of HMA Tools in cal-
culating the composition of an HMA mixture containing RAP.
OCR for page 155
Reclaimed Asphalt Pavement 155
Example Problem 9-1. Gradation and Binder Content Analysis for an
HMA Mixture Containing RAP
A 9.5-mm NMAS mixture will be produced using three new aggregate stockpiles,
hydrated lime, and two RAP stockpiles. Gradation and binder content data for
each stockpile is given in Table 9-1. The stockpiles will be combined in the follow-
ing proportions: 29% of Aggregate 1, 40% of Aggregate 2, 10% of Aggregate 3,
1% lime, 10% Coarse RAP, and 10% Fine RAP. The target VMA should be 16.0%
and the target air void content 4.0%. The specific gravity value for both the new
binder and the RAP binders is 1.030. For this combination of stockpiles, compute
the combined gradation, the binder provided by the RAP, and the amount of
new binder required.
Table 9-1. Stockpile materials for example 1.
Property
Sieve Size, Agg. 1 Agg. 2 Agg. 3 Hydrated Coarse Fine
mm Lime RAP RAP
19.0 100 100 100 100 100 100
12.5 100 100 100 100 100 100
9.5 91 100 100 100 94 100
Gradation,
4.75 19 98 90 100 34 91
% Passing
2.36 6 61 52 100 25 65
1.18 5 37 31 100 22 46
0.600 4 24 20 100 20 34
0.300 4 16 14 100 16 25
0.150 3 8 10 96 12 19
0.075 2.9 3.6 8.4 89 10.4 15.7
Agg. Bulk Spec. Grav. 2.610 2.627 2.619 2.602 2.624 2.614
Agg. App. Spec. Grav. 2.628 2.651 2.645 2.675 2.638 2.637
Binder Content, % --- --- --- --- 3.1 4.5
Solution
The general mix information is entered in the worksheet
Table 9-2.
"General"; this must include the target VMA of 16% and
Combined
the target air void content of 4%. The gradation informa- gradation for the
tion and specific gravity values for the aggregates are proposed HMA
entered in the worksheet "Aggregates" and for the RAP mixture for
in the worksheet "RAP_Aggregates." Asphalt binder con- example 1.
tent and other information for the RAP is also entered
Sieve Size, Percent
in this worksheet. The composition of the blend, that is, mm Passing
the weight percentage of each aggregate and the RAP 19 100
materials, is entered in the worksheet "Trial_Blends" as 12.5 100
9.5 97
Trial No. 1. Make sure to enter the target VMA and tar- 4.75 67
get air void content in this worksheet. The total binder 2.36 41
content for the mix is given in cell F43 as 5.46%. Of this 1.18 27
0.60 19
amount, 0.75% is from the RAP (cell F143) and 4.72% 0.30 14
from the new binder (cell F145). The combined gradation 0.15 9
for this example problem is given in Table 9-2. 0.075 6.6
OCR for page 156
156 A Manual for Design of Hot Mix Asphalt with Commentary
Limiting Variability in HMA Mixes Containing RAP
Because the variability of the RAP properties in a given stockpile can be quite large, it is
important to estimate this variability and make sure that the addition of the RAP to an HMA
mixture will not cause unacceptable increases in production variability. Controlling variability
in mixes containing RAP involves three steps:
1. Sampling RAP stockpiles, as described previously.
2. Calculating the standard deviation for aggregate percent passing and binder content for all
RAP stockpiles.
3. Estimating the maximum amount of RAP that can be added to the mix without exceeding
allowable production variability.
The variability of a mixture of several components, such as HMA, depends on the variability
of the components, the proportions of the components, the precision of the blending, and the
mean value of the components. Calculation of the standard deviation for aggregate gradations
(percent passing) and asphalt content for HMA containing RAP can be quite complicated; as
with other aspects of developing RAP mix designs, the details are not presented here but are included
in the Commentary. The mean and standard deviation values for aggregate gradation and asphalt
binder content are calculated in HMA Tools in the worksheet "RAP_Variability." Data for aggre-
gate gradation and binder content are entered here for up to four RAP stockpiles. Data for up to
30 specimens can be entered for each of these four stockpiles. If no more than 15% RAP is to be
used in a mix design, there is no need to perform a variability analysis of the RAP stockpiles used
in the mix design.
The standard deviation values calculated in the worksheet "RAP_Variability" are only esti-
mates of the true values. There is a 50% chance that the true standard deviation for a given
RAP stockpile will be higher than the calculated value. There is a relatively small chance that
the true standard deviation will be much, much higher than the estimated value. Because the
standard deviation values calculated for the RAP stockpiles are only estimates, the values used
by HMA Tools in determining the maximum allowable RAP content is an upper confidence
limit, rather than the calculated value. In cell B6, the reliability (confidence) level for this esti-
mate is entered; a value of 80% is suggested. The more samples used in calculating the stan-
dard deviation, the more accurate the estimate will be and the lower the value of upper confi-
dence limit for the standard deviation. Therefore, it is suggested that at least five samples be
used for calculating the mean and standard deviation for a RAP stockpile. Larger numbers of
samples--up to 30--will provide greater accuracy and will normally allow greater percentages
of RAP to be used in the mix design.
In using HMA Tools to perform a variability analysis of RAP stockpiles, gradation data for
up to 30 samples for the first RAP stockpile are entered in cells B19:AE31; asphalt content is
entered in cells B33:AE33. Gradation data for up to three more RAP stockpiles are entered in
cell ranges immediately below this. The approximate proportions to which the stockpiles will
be blended must be entered in cells B9:B12. The estimated maximum allowable RAP content
will appear in cell B14 when data entry is complete and the calculation is completed. Because
up to 15% RAP can be used in any HMA design without performing a variability analysis, the
maximum allowable RAP content will never go below 15%. Similarly, since handling large
amounts of RAP during HMA production is often difficult for practical reasons, HMA Tools
limits the maximum allowable RAP to 50%. If needed, the average percent passing and stan-
dard deviation for percent passing for the first RAP stockpile can be read in cells AH19:AH31
and AI19:AI31, respectively. The average and standard deviation of the asphalt binder content
OCR for page 157
Example Problem 9-2. Calculation of Mean, Standard Deviation,
and Maximum Allowable RAP Content for a Single RAP Stockpile
A 30,000-ton RAP stockpile was constructed using millings from several projects.
Table 9-3 summarizes the results of binder content and gradation tests on 10 ran-
dom samples from the stockpile. Calculate the mean, the standard deviation, and
the 80% upper confidence limit of the standard deviation for percent passing.
Also, using HMA Tools determine the maximum allowable RAP content for this
RAP stockpile.
Table 9-3. Results of binder content and gradation tests on
RAP stockpile for example 2.
Sieve Sample Number
Property Size,
1 2 3 4 5 6 7 8 9 10
mm
19.0 100 100 100 100 100 100 100 100 100 100
12.5 98 100 100 99 99 100 100 100 98 98
9.5 91 98 100 94 97 97 95 93 94 94
4.75 67 77 75 71 73 78 75 69 70 72
Gradation, 2.36 53 59 55 54 58 59 57 50 52 53
% Passing 1.18 39 44 48 43 49 46 45 41 39 41
0.600 32 38 37 35 39 36 37 33 32 33
0.300 22 27 25 23 26 23 25 21 22 22
0.150 14 17 16 15 16 14 15 14 13 15
0.075 10.7 12.2 11.9 10.7 12.9 10.3 11.9 10.5 9.8 10.8
Asphalt Content, % 4.0 4.5 4.7 4.4 5.1 4.6 4.6 4.3 4.6 4.8
Solution
The values for percent passing and asphalt binder content given in Table 9-3 are
entered in cells B19:K31 and B33:K33 in the worksheet "RAP_Variability." The
reliability level in cell B6 should be the default value of 80%. Only one RAP stock-
pile is being used, so 100 is entered in cell B9, and cells B10:B12 are left blank.
After calculation (press F9 to make sure HMA_Tools performs the needed calcula-
tions), the mean values are given in cells AH19:AH31 and AH33, the standard
deviation values are given in cells AI19:AI31 and AI33, and the values for the
upper confidence limit for standard deviation are given in cells AJ19:AJ31 and
AJ33. Values for average, standard deviation, and the upper confidence limit for
standard deviation are listed in Table 9-4. The maximum allowable RAP content
of 42% appears in cell B19.
Table 9-4. Computed averages and standard
deviations for the RAP stockpile for example 2.
Standard Upper Confidence
Property Sieve Size, Average Deviation Limit for Std. Dev.
mm
19.0 100.9 0.00 0.00
12.5 99.2 0.92 1.19
9.5 95.3 2.67 3.45
4.75 72.7 3.56 4.61
Gradation, % 2.36 55.0 3.13 4.04
Passing: 1.18 43.5 3.54 4.57
0.600 35.2 2.57 3.33
0.300 23.6 2.01 2.60
0.150 14.9 1.20 1.55
0.075 11.2 0.99 1.28
Asphalt Binder
--- 4.56 0.295 0.382
Content, Wt. %
OCR for page 158
158 A Manual for Design of Hot Mix Asphalt with Commentary
appear in cells AH33 and AI33, respectively. The average and standard deviation of the per-
cent passing and binder content for up to three additional RAP stockpiles appear immediately
below these cells.
Determining Maximum Allowable RAP Content Based on Variability
Using a Graphical Approach
Instead of using HMA Tools, a graphical approach can be used to determine the maximum
allowable RAP content in an HMA mix design. Figures 9-3 through 9-6 are design charts for
estimating the maximum allowable RAP content for an HMA mix design, based on the vari-
ability in gradation and asphalt binder content of the RAP. Figure 9-3 gives the maximum RAP
content based on the standard deviation for aggregate percent passing for a single RAP stock-
pile. Figure 9-4 gives estimated maximum RAP content based on the standard deviation for
asphalt binder content for a single RAP stockpile. Figure 9-5 gives estimated maximum RAP
content based on the average standard deviation for aggregate percent passing for a blend of
RAP stockpiles, while Figure 9-6 gives estimated maximum RAP content based on the average
Standard Deviation for RAP Aggregate % Passing
0 1 2 3 4 5 6 7 8 9 10
50
Max. RAP Content, Wt. %
45
40
35
30
25
20
15
Sieve size, mm: 0.075 0.150 0.300 1.18 4.75 > 9.5
& 0.600 & 2.36 & 9.5
Figure 9-3. Maximum RAP content as a function of standard deviation
for aggregate percent passing. For n = 5 Samples from a single RAP
stockpile.
50
Max. RAP Content, Wt. %
45
40
35
30
25
20
15
0.2 0.3 0.4 0.5 0.6 0.7
Binder Standard Deviation
Figure 9-4. Maximum RAP content as a function of standard deviation
for asphalt binder content. For n = 5 Samples from a single RAP stockpile.
OCR for page 159
Reclaimed Asphalt Pavement 159
Average Standard Deviation for RAP Aggregate % Passing
0 1 2 3 4 5 6 7 8 9 10
50
45
Max. RAP Content, Wt. %
40
35
30
25
20
15
Sieve size, mm: 0.075 0.150 0.300 1.18 4.75 > 9.5
& 0.600 & 2.36 & 9.5
Figure 9-5. Maximum RAP content as a function of average standard deviation
for aggregate percent passing. For n = 5 Samples from a blend of RAP stockpiles,
and no stockpile making up more than 70% of the RAP blend.
50
Max. RAP Content, Wt. %
45
40
35
30
25
20
15
0.2 0.3 0.4 0.5 0.6 0.7
Average Binder Standard Deviation
Figure 9-6. Maximum RAP content as a function of average standard deviation
for asphalt binder content. For n = 5 Samples from a blend of RAP stockpiles, and
no stockpile making up more than 70% of the RAP blend.
standard deviation for asphalt binder content for a blend of RAP stockpiles. Figures 9-5 and 9-6
are different from 9-3 and 9-4 because, when several RAP stockpiles are blended, the variabil-
ity in the resulting blend will tend to be significantly lower than the variability in the individ-
ual stockpiles. Figures 9-5 and 9-6 are based on the assumption that no RAP stockpile in the
RAP blend will make up more than 70% of the RAP blend; if this assumption is not correct, Fig-
ures 9-3 and 9-4 should be used with the standard deviation values for the stockpile making up
most of the RAP blend. All four charts are based on statistics calculated from five independent
samples; they cannot be used for smaller sample sizes. These charts can be used for statistics cal-
culated using more than five samples, but doing so will tend to underestimate the amount of
RAP that can be used in the mix design.
To use these charts, the maximum allowable RAP must be determined for each sieve size for
which the percent passing is less than 100%. The maximum allowable RAP must also be determined
for the asphalt binder content. The maximum allowable RAP content is then the lowest of all these
individual values. The procedure is probably best illustrated with an example problem.
OCR for page 160
160 A Manual for Design of Hot Mix Asphalt with Commentary
Example Problem 9-3. Determination of Maximum Allowable RAP Content
Based on Variability Analysis Using the Graphical Approach
Using the standard deviation values for aggregate percent passing and asphalt
binder content calculated for Example 2, estimate the maximum allowable RAP
content based on variability using Figures 9-3 and 9-4.
Solution
Table 9-5 lists the average percent passing and standard deviation for percent pass-
ing for the RAP stockpile first introduced in Example 2. This also shows the average
and standard deviation for asphalt binder content. The last column in Table 9-5
shows the maximum allowable RAP content based on variability for each individual
sieve and asphalt binder content, as determined using Figures 9-3 and 9-4. The val-
ues range from 30 to 50%; the lowest value is 30% (for the 1.18-mm sieve and the
asphalt binder content); therefore, the overall maximum allowable RAP content
based on variability is 30%. Note that this percentage is significantly less than the
42% found in Example 2 for the same standard deviation values. The value deter-
mined using the graphical approach is lower because it is based on a sample size of
n = 5. As mentioned above, using Figures 9-3 through 9-6 for cases where samples
sizes larger than 5 are used to calculate standard deviation values will provide lower
estimates of maximum allowable RAP content than would be found using more
accurate methods such as the HMA Tools spreadsheet.
Table 9-5. Standard deviation values and
estimated maximum allowable RAP content for
example 3.
Maximum
Standard Allowable RAP
Property Sieve Size, Average Deviation Content
mm %
19.0 100.9 0.00 50
12.5 99.2 0.92 50
9.5 95.3 2.67 50
4.75 72.7 3.56 40
Gradation, % 2.36 55.0 3.13 38
Passing: 1.18 43.5 3.54 30
0.600 35.2 2.57 38
0.300 23.6 2.01 50
0.150 14.9 1.20 50
0.075 11.2 0.99 50
Asphalt Binder
Content, Wt. % --- 4.56 0.295 30
Maximum Allowable RAP Content for Stockpile: 30
Maximum RAP Content, Variability and Binder Properties
The methods described above for estimating maximum allowable RAP content are based
only on variability analysis--the maximum values for RAP content determined in this way only
provide an estimate of how much RAP can be used in a mix design without significantly increasing
production variability. These maximum values do not address the equally important issue of how
the RAP content will affect the final binder grade in the HMA mix. The asphalt binder contained
